1. Field of the Invention
The present invention relates generally to an improved ball nut for use in combination with ball screws to give a positioning assembly. More particularly, it relates to such a ball nut in which abrupt changes in direction in a return path for ball bearings in the ball nut are avoided. Most especially, it relates to such a ball nut with an internal return path.
2. Description of the Prior Art
In conventional ball screw assemblies, a ball nut travels along a lead screw. Ball bearings are positioned between one or more sets of helical threads on an inside surface of the ball nut and corresponding helical threads on the lead screw. The ball nut and lead screw threads form a race for the ball bearings positioned between the threads. The ball bearings move in rolling contact in the threads as the lead screw and the ball nut are rotated with respect to one another. As the lead screw and the ball nut rotate with respect to one another, the ball bearings travel along the helical threads on the inside surface of the ball nut, are removed at one end of those helical threads by a pick-off member and are delivered by a return path to an opposite end of the helical threads, so that the ball bearings are constantly recirculated in the race as the lead screw and ball nut continue to rotate with respect to each other. Ball screw assemblies having both external and internal return paths are known in the art.
Examples of prior art ball screw assemblies are shown in the following issued U.S. Pat. Nos.: 3,902,377, issued Sept. 2, 1975 to Lemor; 4,074,585, issued Feb. 21, 1978 to Richaud et al.; 4,074,587, issued Feb. 21, 1978; U.S. Pat. No. 4,138,902, issued Feb. 13, 1979 and 4,186,620, issued Feb. 5, 1980, all to Brusasco; U.S. Pat. No. 4,211,125, issued Jul. 8, 1980 to Benton; U.S. Pat. No. 4,258,584, issued Mar. 31, 1981 to Haegele et al.; U.S. Pat. No. 4,274,297, issued Jun. 23, 1981 to Blaurock et al.; U.S. Pat. No. 4,357,838, issued Nov. 9, 1982 to Blaurock et al.; U.S. Pat. No. 4,439,011, issued Mar. 27, 1984 to Machmerth; U.S. Pat. No. 4,660,431, issued Apr. 28, 1987 to Heine and U.S. Pat. No. 4,896,552, issued Jan. 30, 1990 to Virga. As disclosed in these issued patents, it is known in such ball screw assemblies to provide a pick-off for the ball bearings at the entrance to the return path which is tangential to the helical threads forming the race between the ball nut and the lead screw. However, the prior art structures for providing tangential pick-offs are complex and expensive.